1. Field of the Invention
The present invention relates to a compression/decompression technique, in particularly, to an image compression/decompression technique.
2. Description of Related Art
In the field of liquid crystal display (LCD) technology, overdriving technique is usually applied in improving the responding time of liquid crystal. To apply the said overdriving technique, a memory unit needs to be disposed in the LCD, so as to store image data for comparison. Detailed descriptions and drawings of the LCD overdriving technique are provided below.
FIG. 1 illustrates a schematic view of an overdriving device of a LCD. Referring to FIG. 1, a memory unit 100 is used for storing a current frame and providing a previous frame to an overdriving unit 110. The overdriving unit 110 may compensate the current frame based on the previous frame, and thereby generate an output frame. To be more specific, the overdriving unit 110 may receive the frames of the current period and the previous period, and generate the output frame according to a Lookup Table.
It is noted that the trend in the LCD industry is to develop LCD with large-sized panel and high-resolution images. The frame data to be stored in the memory unit 100 is becoming larger. As a consequence, the capacity of the memory unit 100 needs to be increased. Inevitably, the costs for producing the LCD are greatly increased as well.
To keep down the costs, a conventional technique has been provided for reducing the data size of a frame. Referring to FIG. 1, this technique is to divide a gray-scale value of each pixel in the frame into a plurality of most significant bits (called MSB hereafter) and a plurality of least significant bits (called LSB hereafter).
More specifically, provided that the gray-scale value of each pixel in the frame is 8 bits, the preceding 4 bits may be considered as the MSB and the succeeding 4 bits may be considered as the LSB. The memory unit 100 may store only the 4 MSB of each pixel in the frame and omit the 4 LSB. Because the gray-scale values of the 4 LSB are 0000˜1111 (0˜15 in decimal system), omission of the 4 LSB would make the error range of the gray-scale value of each pixel in the frame fall between 0˜15. Accordingly, if 5 LSB are omitted, the error range of the gray-scale value would be between 0˜31. In other words, the data size of the frame would be reduced if more LSB are omitted. However, the error range of the frame would be increased correspondingly.